Recently, there has been a great demand for high quality visual services over wireless networks. However, the received video quality is still inadequate due to bandwidth constraints, high error rates and the time varying nature of the channels. In particular, delay constraints for interactive real time video applications, such as video conferencing, make it even more difficult to effectively encode and transmit the video signal. In addition, in video communications and/or storage, there are some unique conditions for both source coding and transmission. With video messaging, a one-way communication, the encoder is allowed to have much more delay, and can take advantage of this for effective coding. In transmission, a re-transmission-based error control technique such as automatic retransmission query (ARQ) can be used between messaging servers. Still, forward error control (FEC) and error concealment based provisions for error resilience are required for mobile users trying to access a messaging server over the wireless network. This is because the mobile users may not be able to store a whole video message, due to the limitation of storage capacity of portable decoder. The bit rate for video messaging should be low, conventionally in the range of 20˜60 kbps, in order to avoid excessive occupancy of the wireless channel as well as storage device of messaging servers. Therefore, an effective coding and error control scheme for video communications, messaging and/or data storage is required.
Although there has been significant progress in waveform-based digital video coders such as block based Motion Compensated Discrete Cosine Transform (MC DCT) [as discussed in the ITU-T, Draft Recommendation H.263: Video Coding for low bit rate communication, incorporated herein by reference], object-based coding approaches to represent video content have concurrently emerged. However, these approaches are characterized by computationally intensive algorithms for accurately segmenting objects, and, in some cases, a heavy outlay of bits for representing arbitrary shapes of objects. A hybrid approach which blends waveform-based coding with object-oriented techniques can improve subjective quality with a useful complexity-delay tradeoff. [Such approaches are discussed, for example, in J. Hartung, et al.,” Object-Oriented H.263 Compatible Video Coding Platform for Conferencing Applications.”, IEEE Journal on Selected Areas in Communication, vol. 16, No.1, January 1998, incorporated herein by reference, and in D. E. Pearson, “Developments in model-based video coding”, Proc. IEEE, vol. 83, June 1995, incorporated herein by reference.] This approach is particularly appropriate for meeting the needs of the wireless messaging system. However, such earlier work has tried to improve video quality by segmenting objects and using object-based rate control for H.263 video. Since finer quantization step size is used for the main object in the scene, the subjective quality of video was shown to increase noticeably. However, this work did not explicitly address error resilience. In other work [see for example P. Batra and S. F. Chang, “Effective Algorithms for Video Transmission over Wireless Channel”, Intern. Journal of Image Communication: Signal Processing, Special Issue on Moble Image/Video Transmission, 1998, incorporated herein by reference], a content based approach is used for unequal resource allocation for error protection. However, the meaning of “content” in that work was not the object in a video scene, but the syntax of video bit stream such as header, motion vectors and discrete cosine transform (DCT) coefficients. Therefore, a need exists in the industry to communicate and/or store video data with a higher degree of reliability and accuracy.